This invention relates to cranes having booms and extensions connected thereto and in particular to such extensions which have the capability of being fixed at a plurality of distinct angles of offset in a vertical plane and relative to the center line of the crane boom.
A previous offset boom arrangement is shown in the Mentzer U.S. Pat. No. 4,484,686, which discloses a slotted tension link arrangement wherein a pin is allowed to slide freely in the slot when the boom extension is in a certain position, and require high manufacturing and holding tolerances.
Another example is the Miller U.S. Pat. No. 3,085,695, which shows a crane boom with a hinge arrangement and a multi-position linkage that allows the different parts of the boom to assume a plurality of relative angles. This arrangement is not easily adaptable to an existing crane boom since the upper crane connection described therein would not work without the link arrangement of that invention.
The present invention relates to improvements over the apparatus described above and to solutions to the problems raised thereby.